Mechanical abrasion of logs in a pilot tumble debarking drum

摘要

This paper presents the parameters affecting the mechanical abrasion of logs in tumble debarking, together with information on the debarking mechanism. As research into the real process is difficult due to changing process conditions and difficulties in marking the logs properly, a pilot-scale drum was used. Since no actual loosening of the bark occurs in a pilot-scale drum, the mechanism was studied indirectly by wrapping carbon paper around the logs and tracing the marks of mechanical abrasion on this by scanning and image analysis. This allowed the total mechanical abrasion (total colour of the carbon paper) and the proportion of blows and shear forces (the distribution of colour on the carbon paper) to be analysed. Total mechanical abrasion correlated closely with the residence time of the log, and was increased by the use of longer logs, increased capacity, a lower degree of filling and greater rotating speed of the drum. Blows occurred mainly at the ends of the logs and shear forces on the sides. The results can be used in connection with the real process to control the debarking result on the basis of residence time. It has been shown earlier how the process parameters affect the residence time of logs. Controlling the residence time makes it possible to adapt the debarking efficiency to wood quality, allowing the required log cleanness to be achieved with smaller wood losses, which is important for process profitability.